1. Field of the Invention
The present invention relates to a substrate coated with a hard carbon film which is applicable to a cutter such as an electric shaver or a thin-film head, and a method of and an apparatus for forming the same.
2. Description of the Background Art
In order to improve adhesion between a substrate such as a ceramic substrate or a silicon substrate and a diamond-like carbon film, it has generally been proposed to form an intermediate layer between the substrate and the diamond-like carbon film. Japanese Patent Laying-Open No. 1-317197 (1989) discloses a technique of forming an intermediate layer mainly composed of silicon on a substrate by plasma CVD, and then forming a diamond-like carbon film on the intermediate layer. The intermediate layer improves the adhesion of the diamond-like carbon film to the substrate as compared with the case of directly forming a diamond-like carbon film on a substrate.
However, no studies have been conducted relating to the formation of an intermediate layer between a diamond-like carbon film and a substrate of nickel (Ni), aluminum (Al) or stainless steel for application to a cutter such as an electric shaver cutter.
On the other hand, an apparatus described in Japanese Patent Laying-Open No. 3-175620 (1991) is known for forming a hard carbon film by plasma CVD. This apparatus is adapted to form a diamond-like carbon film, which is a hard carbon film, on a substrate by bias plasma CVD employing an ECR (electron cyclotron resonance) plasma CVD apparatus.
FIG. 12 typically illustrates such a conventional apparatus for forming a diamond-like carbon film. Referring to FIG. 12, microwave supply means 1 generates a microwave that passes through a waveguide 2 and a microwave inlet window 3 to be guided to a plasma generation chamber 4. This plasma generation chamber 4 is provided with a discharge gas inlet pipe 5 for introducing a discharge gas such as argon (Ar) gas. Further, a plasma magnetic field generator 6 is provided around the plasma generation chamber 4. Due to the action of a high-frequency magnetic field which is formed by the microwave and a magnetic field generated by the plasma magnetic field generator 6, a plasma of high density is formed in the plasma generation chamber 4. This plasma is guided to a vacuum chamber 8 in which a substrate 7 is arranged, along the magnetic field diverged by the plasma magnetic field generator 6.
The vacuum chamber 8 is provided therein with a reaction gas inlet pipe 9 for introducing methane (CH.sub.4) gas serving as a raw material gas. The methane gas which is introduced into the vacuum chamber 8 by the reaction gas inlet pipe 9 is decomposed by action of the plasma, to form a carbon film. A high-frequency power source 10, with a frequency of 13.56 MHz, for example, is provided externally of the vacuum chamber 8 for applying a prescribed high-frequency voltage (RF voltage) to a substrate holder 11, thereby developing a negative self-bias in the substrate 7. Ions travel in the plasma at a lower speed than electrons, and hence, unlike the electrons, the ions cannot follow the potential deflection during application of the RF voltage. Thus, a large quantity of electrons are emitted toward the substrate 7 due to application of the RF voltage, whereby a negative self-bias is developed in the substrate 7. Thus, positive ions contained in the plasma are drawn to form a diamond-like carbon film on the substrate 7.
In such a conventional apparatus, the substrate 7 is mounted on the substrate holder 11 which is provided in the vacuum chamber 8, and thereafter the vacuum chamber 8 is evacuated for forming a film. Thus, this apparatus can treat only one substrate, or two substrates at the most, in a single film forming operation.
In the conventional apparatus, further, discharge is also caused in the vicinity of a portion of the substrate that is mounted on the substrate holder, i.e. a portion of the substrate that is not to be provided with a film. This effect disadvantageously increases the temperature of the substrate.